Understanding Aqueous
Dispersibility of Graphene Oxide
and Reduced Graphene Oxide through p<i>K</i><sub>a</sub> Measurements
- Publication date
- Publisher
Abstract
The chemistry underlying the aqueous dispersibility of
graphene
oxide (GO) and reduced graphene oxide (r-GO) is a key consideration
in the design of solution processing techniques for the preparation
of processable graphene sheets. Here, we use zeta potential measurements,
pH titrations, and infrared spectroscopy to establish the chemistry
underlying the aqueous dispersibility of GO and r-GO sheets at different
values of pH. We show that r-GO sheets have ionizable groups with
a single p<i>K</i> value (8.0) while GO sheets have groups
that are more acidic (p<i>K</i> = 4.3), in addition to groups
with p<i>K</i> values of 6.6 and 9.0. Infrared spectroscopy
has been used to follow the sequence of ionization events. In both
GO and r-GO sheets, it is ionization of the carboxylic groups that
is primarily responsible for the build up of charge, but on GO sheets,
the presence of phenolic and hydroxyl groups in close proximity to
the carboxylic groups lowers the p<i>K</i><sub>a</sub> value
by stabilizing the carboxylate anion, resulting in superior water
dispersibility